The present invention relates to a method for providing power control and rate information in a mobile radio communication system, and in particular, the method is suitable for use in the UMTS Terrestrial Radio Access (UTRA) system where UMTS stands for Universal Mobile Telecommunication System. In the UTRA system a variety of different services are provided where a service can be characterised by a combination of transmission rate and bit reliability. Therefore, there is a requirement for radio links between the mobile terminal and the base station to be able to carry one or more different services contemporaneously. From time to time it may be necessary to alter the service mix passing over the channel and this alteration in service mix can lead to a change in the required transmission rate, and therefore the capability of altering the transmission rate is provided.
The UTRA system is based upon spread spectrum Code Division Multiple Access (CDMA) technology. There are two mechanisms employed for altering the bit rate, the first is to alter the spreading factor applied to a code that is transmitted over the radio channel, the second degree of freedom is to alter the number of codes which are added together prior to transmission. For a given multiplex the current rate of transmission needs to be communicated from the mobile station to the base station when considering the uplink.
An aim of the present invention is to provide a method of power control and rate information signalling in a mobile communications system.
According to the present invention there is provided a method of operating an uplink of a CDMA mobile telecommunications system, comprising the steps of:
communicating transmission rate information from a mobile station to a base station by transmitting rate information data in a frame for either the frame in which said rate information data was transmitted (Mode A), or for a subsequent frame (Mode B),
optimising performance by switching between Modes A and B,
with respect to Mode A, arranging for the base station to measure a received signal to interference ratio (SIR) independently of the transmission rate of the data,
with respect to Mode B, arranging for the base station to measure the SIR in dependence upon the information rate of the received data, and,
using the measured SIR to effect control of the transmission power of the mobile station.
According to an aspect of the present invention, a signal amenable to measurement of its SIR independently of the rate information for that frame is transmitted using a specific spread spectrum code, and applied either to an inphase or quadrature channel within its transmit signal generation path in the mobile station prior to the application of any further processing in said path.
According to a further aspect of the present invention, the mode selection is made by transmitting to all terminals operating in a cell, information on a control channel which states the mode of operation.